Field
The present invention relates to a molded article comprising a polyamide resin composition.
Description of the Related Art
Polyamide resins are excellent in strength, heat resistance, and chemical resistance and have a smaller specific gravity than that of metals. Therefore, the polyamide resins have heretofore been used as alternative materials for metals in automobile mechanical parts, etc.
In recent years, the downsizing of automobiles has been practiced as one approach for improvement in fuel efficiency. As a result, automobile engine room parts tend to have a higher density, and engine rooms tend to have a higher internal ambient temperature. In addition, higher powers have been imparted to engines with superchargers for improvement in fuel efficiency. Along with this, engine rooms tend to have an increasingly higher ambient temperature.
Thus, there has been a demand for molded articles having excellent mechanical physical properties under higher-temperature conditions than ever. Specifically, there has been a growing demand for molded articles that can maintain practically sufficient mechanical characteristics even when used for a long time under high-temperature conditions of 150° C. to 230° C.
A technique which involves adding a copper compound (an oxide or a salt of copper) is heretofore known as a technique for improving the heat aging resistance of polyamide resins.
Likewise, a technique which involves mixing a copper compound and iron oxide with 2 types of polyamide resins differing in melting point (see e.g., Patent Literature 3), a technique which involves mixing a fine element iron with a polyamide resin (see e.g., Patent Literature 4), and a technique which involves mixing a fine dispersed metal powder with a polyamide resin (see e.g., Patent Literature 5) are reported as techniques for improving the heat aging resistance.
Meanwhile, a polyamide resin composition supplemented with sodium aluminate and a method for producing the same are reported (see e.g., Patent Literatures 6 to 11). The polyamide resin composition supplemented with the sodium aluminate has been known to have excellent heat retention stability.
The “heat retention stability” refers to characteristics by which the polyamide resin is less decomposed and deteriorated when the polyamide resin composition is kept at a temperature equal to or higher than the melting point and is thereby in a melted state, and consequently, reduction in mechanical physical properties or color change of the polyamide resin composition caused by keeping it at the temperature equal to or higher than the melting point is prevented.
Also, a technique which involves supplementing a polyamide resin with a resin having a lower melting point than that of the polyamide resin and a heat stabilizer is reported (see e.g., Patent Literature 3).
A technique which involves mixing a phosphorus compound together with a polyvalent metal compound into a melted polyamide or mixing these compounds in a polyamide production and polymerization step to obtain a polyamide having improved color characteristics has been further reported (see e.g., Patent Literature 12).